Neonatal infection-induced memory impairment after lipopolysaccharide in adulthood is prevented via caspase-1 inhibition

Prenatal immune origins of brain aging differ by sex

With an increasing aging population and Alzheimer's disease tsunami, it is critical to identify early antecedents of brain aging to target for intervention and prevention. Women and men develop and age differently, thus using a sex differences lens can contribute to identification of early risk biomarkers and resilience. There is growing evidence for fetal antecedents to adult memory impairments, potentially through disruption of maternal prenatal immune pathways. Here, we hypothesized that in utero exposure to maternal pro-inflammatory cytokines will have sex-dependent effects on specific brain circuitry regulating offspring's memory and immune function that will be retained across the lifespan. Using a unique prenatal cohort, we tested this in 204 adult offspring, equally divided by sex, who were exposed/unexposed to an adverse in utero maternal immune environment and followed into early midlife (~age 50). Functional magnetic resonance imaging results showed exposure to pro-inflammatory cytokines in utero (i.e., higher maternal IL-6 and TNF-α levels) was significantly associated with sex differences in brain activity and connectivity underlying memory circuitry and performance and with a hyperimmune state, 50 years later. In contrast, the anti-inflammatory cytokine, IL-10 alone, was not significantly associated with memory circuitry in midlife. Predictive validity of prenatal exposure was underscored by significant associations with age 7 academic achievement, also associated with age 50 memory performance. Results uniquely demonstrated that adverse levels of maternal in utero pro-inflammatory cytokines during a critical period of the sexual differentiation of the brain produced long-lasting effects on immune function and memory circuitry/function from childhood to midlife that were sex-dependent, brain region-specific, and, within women, reproductive stage-dependent.

Lipopolysaccharide differentially alters systemic and brain glucocorticoid levels in neonatal and adult mice

Glucocorticoids (GCs) are secreted by the adrenal glands and increase in response to stressors (e.g., infection). The brain regulates local GC levels via GC synthesis, regeneration and/or metabolism. Little is known about local GC regulation within discrete brain regions at baseline or in response to stress. We treated male and female C57BL/6J mice at postnatal day 5 (PND5) or PND90 with lipopolysaccharide (LPS; 50 μg/kg bw i.p.) or vehicle and collected blood and brain after 4 h. We microdissected the prefrontal cortex, hippocampus, hypothalamus and amygdala. We measured seven steroids, including corticosterone, via liquid chromatography-tandem mass spectrometry and measured transcripts for key steroidogenic enzymes (Cyp11b1, Hsd11b1, Hsd11b2) via qPCR. At both ages, LPS increased GC levels in blood and all brain regions; however, the increases were much greater at PND90 than at PND5. Interestingly, PND5 corticosterone levels were lower in prefrontal cortex than in blood, but higher in amygdala than in blood. These changes in corticosterone levels align with local changes in steroidogenic enzyme expression, demonstrating robust regional heterogeneity and a possible mechanism for the region-specific effects of early-life stress. In contrast, PND90 corticosterone levels were lower in all brain regions than in blood and similar among regions, and steroidogenic enzyme mRNA levels were generally not affected by LPS. Together, these data indicate that local GC levels within discrete brain regions are more heterogeneous at baseline and in response to LPS at PND5 than at PND90, as a result of increased local GC production and metabolism in the neonatal brain.

Maternal prenatal immune activation associated with brain tissue microstructure and metabolite concentrations in newborn infants

Few human studies have assessed the association of prenatal maternal immune activation (MIA) with measures of brain development and psychiatric risk in newborn offspring. Our goal was to identify the effects of MIA during the 2nd and 3rd trimesters of pregnancy on newborn measures of brain metabolite concentrations, tissue microstructure, and motor development. This was a prospective longitudinal cohort study conducted with nulliparous pregnant women who were aged 14 to 19 years and recruited in their 2nd trimester, as well as their children who were followed through 14 months of age. MIA was indexed by maternal interleukin-6 (IL-6) and C-reactive protein (CRP) in both trimesters of pregnancy. Primary outcomes included: (1) newborn brain metabolite concentrations as ratios to creatine (N-acetylaspartate (NAA)/creatine (Cr) and choline (Cho)/Cr) measured using Magnetic Resonance Spectroscopy; (2) newborn fractional anisotropy and mean diffusivity, measured using Diffusion Tensor Imaging; and (3) indices of motor development, assessed prenatally and postnatally at ages 4- and 14-months. Maternal IL-6 and CRP levels associated significantly with both metabolites in the putamen, thalamus, insula, and the internal capsule. Maternal IL-6 associated significantly with fractional anisotropy in the putamen, caudate, thalamus, insula, and precuneus, and with mean diffusivity in the inferior parietal and middle temporal gyrus. CRP associated significantly with fractional anisotropy in the thalamus, insula, and putamen. Significant associations were found in common regions across imaging modalities, though the direction of associations differed by immune marker. In addition, both maternal IL-6 and CRP (in both trimesters) prenatally associated significantly with offspring motor development at 4- and 14-months of age. The left thalamus mediated effects of IL-6 on postnatal motor development. These findings demonstrate that levels of MIA in mid- to late pregnancy in a generally healthy sample associate with tissue characteristics in newborn brain regions that primarily support motor integration and coordination, as well as behavioral regulation. Those brain effects may contribute to differences in motor development.

Acute postnatal inflammation alters adult microglial responses to LPS that are sex-, region- and timing of postnatal inflammation-dependent

BACKGROUND

Adverse events in early life can have impact lasting into adulthood. We investigated the long-term effects of systemic inflammation during postnatal development on adult microglial responses to lipopolysaccharide (LPS) in two CNS regions (cortex, cervical spinal cord) in male and female rats.

METHODS

Inflammation was induced in Sprague-Dawley rats by LPS (1 mg/kg) administered intraperitoneally during postnatal development at P7, P12 or P18. As adults (12 weeks of age), the rats received a second LPS dose (1 mg/kg). Control rats received saline. Microglia were isolated 3 h post-LPS followed by gene expression analysis via qRT-PCR for pro-inflammatory (IL-6, iNOS, Ptgs2, C/EBPb, CD14, CXCL10), anti-inflammatory (CD68, Arg-1), and homeostatic genes (P2Y12, Tmemm119). CSF-1 and CX3CL1 mRNAs were analyzed in microglia-free homogenates.

RESULTS

Basal gene expression in adult microglia was largely unaffected by postnatal inflammation. Adult cortical microglial pro-inflammatory gene responses to LPS were either unchanged or attenuated in rats exposed to LPS during postnatal development. Ptgs2, C/EBPb, CXCL10 and Arg-1 were the most affected genes, with expression significantly downregulated vs. rats without postnatal LPS. Spinal microglia were affected most by LPS at P18, with mixed and sometimes opposing effects on proinflammatory genes in males vs. females. Overall, male cortical vs. spinal microglia were more affected by postnatal LPS. Females were affected in both cortex and spinal cord, but the effect was dependent on timing of postnatal LPS. Overall, inflammatory challenge at P18 had greater effect on adult microglia vs. challenge at P12 or P7.

CONCLUSIONS

Long-lasting effects of postnatal inflammation on adult microglia depend on postnatal timing, CNS region and sex.

Kojic acid reverses LPS-induced neuroinflammation and cognitive impairment by regulating the TLR4/NF-κB signaling pathway

Intense neuroinflammation contributes to neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease. Lipopolysaccharides (LPSs) are an integral part of the cell wall of Gram-negative bacteria that act as pathogen-associated molecular patterns (PAMPs) and potentially activate the central nervous system's (CNS) immune system. Microglial cells are the local macrophages of the CNS and have the potential to induce and control neuroinflammation. This study aims to evaluate the anti-inflammatory and antioxidant effect of kojic acid against the toxic effects of LPSs, such as neuroinflammation-induced neurodegeneration and cognitive decline. The C57BL/6N mice were subjected to LPS injection for 2 weeks on alternate days (each mouse received 0.25 mg/kg/i.p. for a total of seven doses), and kojic acid was administered orally for 3 weeks consecutively (50 mg/kg/mouse, p. o). Bacterial endotoxins, or LPSs, are directly attached to TLR4 surface receptors of microglia and astrocytes and alter the cellular metabolism of immune cells. Intraperitoneal injection of LPS triggers the toll-like receptor 4 (TLR4), phospho-nuclear factor kappa B (p-NFκB), and phospho-c-Jun n-terminal kinase (p-JNK) protein expressions in the LPS-treated group, but these expression levels were significantly downregulated in the LPS + KA-treated mice brains. Prolong neuroinflammation leads to the generation of reactive oxygen species (ROS) followed by a decrease in nuclear factor erythroid-2-related factor 2 (Nrf2) and the enzyme hemeoxygenase 1 (HO-1) expression in LPS-subjected mouse brains. Interestingly, the levels of both Nrf-2 and HO-1 increased in the LPS + KA-treated mice group. In addition, kojic acid inhibited LPS-induced TNF-α and IL-1β production in mouse brains. These results indicated that kojic acid may suppress LPS-induced neuroinflammation and oxidative stress in male wild-type mice brains (in both the cortex and the hippocampus) by regulating the TLR4/NF-κB signaling pathway.

Programmed cell death factor 4-mediated hippocampal synaptic plasticity is involved in early life stress and susceptibility to depression

Early life stress (ELS) increases the risk of depression later in life. Programmed cell death factor 4 (PDCD4), an apoptosis-related molecule, extensively participates in tumorigenesis and inflammatory diseases. However, its involvement in a person's susceptibility to ELS-related depression is unknown. To examine the effects and underlying mechanisms of PDCD4 on ELS vulnerability, we used a "two-hit" stress mouse model: an intraperitoneal injection of lipopolysaccharide (LPS) into neonatal mice was performed on postnatal days 7-9 (P7-P9) and inescapable foot shock (IFS) administration in adolescent was used as a later-life challenge. Our study shows that compared with mice that were only exposed to the LPS or IFS, the "two-hit" stress mice developed more severe depression/anxiety-like behaviors and social disability. We detected the levels of PDCD4 in the hippocampus of adolescent mice and found that they were significantly increased in "two-hit" stress mice. The results of immunohistochemical staining and Sholl analysis showed that the number of microglia in the hippocampus of "two-hit" stress mice significantly increased, with morphological changes, shortened branches, and decreased numbers. However, knocking down PDCD4 can prevent the number and morphological changes of microglia induced by ELS. In addition, we confirmed through the Golgi staining and immunohistochemical staining results that knocking down PDCD4 can ameliorate ELS-induced synaptic plasticity damage. Mechanically, the knockdown of PDCD4 exerts neuroprotective effects, possibly via the mediation of BDNF/AKT/CREB signaling. Combined, these results suggest that PDCD4 may play an important role in the ELS-induced susceptibility to depression and, thus, may become a therapeutic target for depressive disorders.

Hofbauer cells and fetal brain microglia share transcriptional profiles and responses to maternal diet-induced obesity

Maternal immune activation is associated with adverse offspring neurodevelopmental outcomes, many mediated by in utero microglial programming. As microglia remain inaccessible throughout development, identification of noninvasive biomarkers reflecting fetal brain microglial programming could permit screening and intervention. We used lineage tracing to demonstrate the shared ontogeny between fetal brain macrophages (microglia) and fetal placental macrophages (Hofbauer cells) in a mouse model of maternal diet-induced obesity, and single-cell RNA-seq to demonstrate shared transcriptional programs. Comparison with human datasets demonstrated conservation of placental resident macrophage signatures between mice and humans. Single-cell RNA-seq identified common alterations in fetal microglial and Hofbauer cell gene expression induced by maternal obesity, as well as sex differences in these alterations. We propose that Hofbauer cells, which are easily accessible at birth, provide insights into fetal brain microglial programs and may facilitate the early identification of offspring vulnerable to neurodevelopmental disorders.

Impacts of age and environment on postnatal microglial activity: Consequences for cognitive function following early life adversity

Early life adversity (ELA) increases the likelihood of later-life neuropsychiatric disorders and cognitive dysfunction. Importantly, ELA, neuropsychiatric disorders, and cognitive deficits all involve aberrant immune signaling. Microglia are the primary neuroimmune cells and regulate brain development. Microglia are particularly sensitive to early life insults, which can program their responses to future challenges. ELA in the form of maternal separation (MS) in rats alters later-life microglial morphology and the inflammatory profile of the prefrontal cortex, a region important for cognition. However, the role of microglial responses during MS in the development of later cognition is not known. Therefore, here we aimed to determine whether the presence of microglia during MS mediates long-term impacts on adult working memory. Clodronate liposomes were used to transiently deplete microglia from the brain, while empty liposomes were used as a control. We hypothesized that if microglia mediate the long-term impacts of ELA on working memory in adulthood, then depleting microglia during MS would prevent these deficits. Importantly, microglial function shifts throughout the neonatal period, so an exploratory investigation assessed whether depletion during the early versus late neonatal period had different effects on adult working memory. Surprisingly, empty liposome treatment during the early, but not late, postnatal period induced microglial activity changes that compounded with MS to impair working memory in females. In contrast, microglial depletion later in infancy impaired later life working memory in females, suggesting that microglial function during late infancy plays an important role in the development of cognitive function. Together, these findings suggest that microglia shift their sensitivity to early life insults across development. Our findings also highlight the potential for MS to impact some developmental processes only when compounded with additional neuroimmune challenges in a sex-dependent manner.

Combined Effect of Maternal Separation and Early-Life Immune Activation on Brain and Behaviour of Rat Offspring

Adversity during early life, a critical period for brain development, increases vulnerability and can have a lasting impact on the brain and behaviour of a child. However, the long-term effects of cumulative early-life stressors on brain and behaviour are not well known. We studied a 2-hit rat model of early-life adversity using maternal separation (MS) and immune activation (lipopolysaccharide (LPS)). Rat pups underwent MS for 15 (control) or 180 (MS) minutes per day from postnatal day (P)2-14 and were administered saline or LPS (intraperitoneal) on P3. Open-field (OFT) and object-place recognition tests were performed on rat offspring at P33-35 and P42-50, respectively. The pre-frontal cortex (PFC) and hippocampus were removed at the experimental endpoint (P52-55) for mRNA expression. MS induced anxiety-like behaviour in OFT in male and reduced locomotor activity in both male and female offspring. LPS induced a subtle decline in memory in the object-place recognition test in male offspring. MS increased glial fibrillary acidic protein (GFAP) and brain-derived neurotrophic factor expression in PFC and ionised calcium-binding adapter molecule-1 expression in male hippocampus. MS and LPS resulted in distinct behavioural phenotypes in a sex-specific manner. The combination of MS and LPS had a synergistic effect on the anxiety-like behaviour, locomotor activity, and GFAP mRNA expression outcomes.

Hofbauer cells and fetal brain microglia share transcriptional profiles and responses to maternal diet-induced obesity

Maternal immune activation is associated with adverse offspring neurodevelopmental outcomes, many mediated by in utero microglial programming. As microglia remain inaccessible throughout development, identification of noninvasive biomarkers reflecting fetal brain microglial programming could permit screening and intervention. We used lineage tracing to demonstrate the shared ontogeny between fetal brain macrophages (microglia) and fetal placental macrophages (Hofbauer cells) in a mouse model of maternal diet-induced obesity, and single-cell RNA-seq to demonstrate shared transcriptional programs. Comparison with human datasets demonstrated conservation of placental resident macrophage signatures between mice and humans. Single-cell RNA-seq identified common alterations in fetal microglial and Hofbauer cell gene expression induced by maternal obesity, as well as sex differences in these alterations. We propose that Hofbauer cells, which are easily accessible at birth, provide novel insights into fetal brain microglial programs, and may facilitate the early identification of offspring vulnerable to neurodevelopmental disorders in the setting of maternal exposures.

Evaluating different models of maternal stress on stress-responsive systems in prepubertal mice

Introduction

Maternal adversity during pregnancy influences neurodevelopment in human and model animal offspring. Adversity can result from stressors coming from many different directions ranging from environmental to nutritional and physiological to immune (e.g., infection). Most stressors result in fetal overexposure to glucocorticoids that have been directly linked to long- and short-term negative impacts on neurological health of offspring. Neuropsychiatric diseases postulated to have fetal origins are diverse and include such things cardiovascular disease, obesity, affective disorders, and metabolic and immune disorders.

Methods

The experiments in the current study compare 3 stressors: prenatal exposure to dexamethasone (DEX), maternal high fat diet (HFD), and maternal caloric restriction (CR). Offspring of mothers with these treatments were examined prepubertally to evaluate stress responsiveness and stress-related behaviors in in male and female mice.

Results

Prenatal exposure to synthetic glucocorticoid, DEX, resulted in decreased neonatal body weights, reduced social interaction behavior, and hypoactive stress response offspring exposed to maternal DEX. Maternal CR resulted in decreased body weights and social interaction behavior in males and females and increased anxiety-like behavior and acute stress response only in males. HFD resulted in altered body weight gain in both sex offspring with decreased anxiety-like behavior in a female-biased manner.

Discussion

The idea that glucocorticoid responses to different stressors might serve as a common stimulus across stress paradigms is insufficient, given that different modes of prenatal stress produced differential effects. Opposite nutritional stressors produced similar outcomes for anxiety-like behavior in both sexes, social-like behavior in females, and a hyperactive adrenal stress response in males. One common theme among the three models of maternal stress (DEX, CR, and HFD) was consistent data showing their role in activating the maternal and fetal immune response. By tuning in on the more immediate immunological aspect on the developing fetus (e.g., hormones, cytokines), additional studies may tease out more direct outcomes of maternal stress in rodents and increase their translational value to human studies.

The microbiota-gut-brain axis in hippocampus-dependent learning and memory: current state and future challenges

A fundamental shift in neuroscience suggests bidirectional interaction of gut microbiota with the healthy and dysfunctional brain. This microbiota-gut-brain axis has mainly been investigated in stress-related psychopathology (e.g. depression, anxiety). The hippocampus, a key structure in both the healthy brain and psychopathologies, is implicated by work in rodents that suggests gut microbiota substantially impact hippocampal-dependent learning and memory. However, understanding microbiota-hippocampus mechanisms in health and disease, and translation to humans, is hampered by the absence of a coherent evaluative approach. We review the current knowledge regarding four main gut microbiota-hippocampus routes in rodents: through the vagus nerve; via the hypothalamus-pituitary-adrenal-axis; by metabolism of neuroactive substances; and through modulation of host inflammation. Next, we suggest an approach including testing (biomarkers of) the four routes as a function of the influence of gut microbiota (composition) on hippocampal-dependent (dys)functioning. We argue that such an approach is necessary to proceed from the current state of preclinical research to beneficial application in humans to optimise microbiota-based strategies to treat and enhance hippocampal-dependent memory (dys)functions.

Maternal prenatal immune activation associated with brain tissue microstructure and metabolite concentrations in newborn infants

Importance

Few translational human studies have assessed the association of prenatal maternal immune activation with altered brain development and psychiatric risk in newborn offspring.

Objective

To identify the effects of maternal immune activation during the 2nd and 3rd trimesters of pregnancy on newborn brain metabolite concentrations, tissue microstructure, and longitudinal motor development.

Design

Prospective longitudinal cohort study conducted from 2012 - 2017.

Setting

Columbia University Irving Medical Center and Weill Cornell Medical College.

Participants

76 nulliparous pregnant women, aged 14 to 19 years, were recruited in their 2nd trimester, and their children were followed through 14 months of age.

Exposure

Maternal immune activation indexed by maternal interleukin-6 and C-reactive protein in the 2nd and 3rd trimesters of pregnancy.

Main Outcomes and Measures

The main outcomes included (1) newborn metabolite concentrations, measured as N-acetylaspartate, creatine, and choline using Magnetic Resonance Spectroscopy; (2) newborn fractional anisotropy and mean diffusivity measured using Diffusion Tensor Imaging; and (3) indices of motor development assessed prenatally and postnatally at ages 4- and 14-months.

Results

Maternal interleukin-6 and C-reactive protein levels in the 2nd or 3rd trimester were significantly positively associated with the N-acetylaspartate, creatine, and choline concentrations in the putamen, thalamus, insula, and anterior limb of the internal capsule. Maternal interleukin-6 was associated with fractional anisotropy in the putamen, insula, thalamus, precuneus, and caudate, and with mean diffusivity in the inferior parietal and middle temporal gyrus. C-reactive protein was associated with fractional anisotropy in the thalamus, insula, and putamen. Regional commonalities were found across imaging modalities, though the direction of the associations differed by immune marker. In addition, a significant positive association was observed between offspring motor development and both maternal interleukin-6 and C-reactive protein (in both trimesters) prenatally and 4- and 14-months of age.

Conclusions and Relevance

Using a healthy sample, these findings demonstrate that levels of maternal immune activation in mid- to late pregnancy associate with tissue characteristics in newborn brain regions primarily supporting motor integration/coordination and behavioral regulation and may lead to alterations in motor development.

Signalling cognition: the gut microbiota and hypothalamic-pituitary-adrenal axis

Cognitive function in humans depends on the complex and interplay between multiple body systems, including the hypothalamic-pituitary-adrenal (HPA) axis. The gut microbiota, which vastly outnumbers human cells and has a genetic potential that exceeds that of the human genome, plays a crucial role in this interplay. The microbiota-gut-brain (MGB) axis is a bidirectional signalling pathway that operates through neural, endocrine, immune, and metabolic pathways. One of the major neuroendocrine systems responding to stress is the HPA axis which produces glucocorticoids such as cortisol in humans and corticosterone in rodents. Appropriate concentrations of cortisol are essential for normal neurodevelopment and function, as well as cognitive processes such as learning and memory, and studies have shown that microbes modulate the HPA axis throughout life. Stress can significantly impact the MGB axis via the HPA axis and other pathways. Animal research has advanced our understanding of these mechanisms and pathways, leading to a paradigm shift in conceptual thinking about the influence of the microbiota on human health and disease. Preclinical and human trials are currently underway to determine how these animal models translate to humans. In this review article, we summarize the current knowledge of the relationship between the gut microbiota, HPA axis, and cognition, and provide an overview of the main findings and conclusions in this broad field.

Neonatal immune challenge poses a sex-specific risk for epigenetic microglial reprogramming and behavioral impairment

While the precise processes underlying a sex bias in the development of central nervous system (CNS) disorders are unknown, there is growing evidence that an early life immune activation can contribute to the disease pathogenesis. When we mimicked an early systemic viral infection or applied murine cytomegalovirus (MCMV) systemically in neonatal female and male mice, only male adolescent mice presented behavioral deficits, including reduced social behavior and cognition. This was paralleled by an increased amount of infiltrating T cells in the brain parenchyma, enhanced interferon-γ (IFNγ) signaling, and epigenetic reprogramming of microglial cells. These microglial cells showed increased phagocytic activity, which resulted in abnormal loss of excitatory synapses within the hippocampal brain region. None of these alterations were seen in female adolescent mice. Our findings underscore the early postnatal period's susceptibility to cause sex-dependent long-term CNS deficiencies following infections.

Neurodevelopmental outcome of infants who develop necrotizing enterocolitis: The gut-brain axis

Necrotizing enterocolitis (NEC) poses a significant risk for neurodevelopmental impairment in extremely preterm infants. The gut microbiota shapes the development of the gut, immune system, and the brain; and dysbiosis drive neonatal morbidities including NEC. In this chapter, we delineate a gut-brain axis linking gut microbiota to the adverse neurological outcomes in NEC patients. We propose that in NEC, immaturity of the microbiome along with aberrant gut microbiota-driven immaturity of the gut barrier and immune system can lead to effects including systemic inflammation and circulating microbial mediators. This nexus of gut microbiota-driven systemic effects further interacts with a likewise underdeveloped blood-brain barrier to regulate neuroinflammation and neurodevelopment. Targeting deviant gut-brain axis signaling presents an opportunity to improve the neurodevelopmental outcomes of NEC patients.

Neonatal inflammation increases hippocampal KCC2 expression through methylation-mediated TGF-β1 downregulation leading to impaired hippocampal cognitive function and synaptic plasticity in adult mice

The mechanisms by which neonatal inflammation leads to cognitive deficits in adulthood remain poorly understood. Inhibitory GABAergic synaptic transmission plays a vital role in controlling learning, memory and synaptic plasticity. Since early-life inflammation has been reported to adversely affect the GABAergic synaptic transmission, the aim of this study was to investigate whether and how neonatal inflammation affects GABAergic synaptic transmission resulting in cognitive impairment. Neonatal mice received a daily subcutaneous injection of lipopolysaccharide (LPS, 50 μg/kg) or saline on postnatal days 3-5. It was found that blocking GABAergic synaptic transmission reversed the deficit in hippocampus-dependent memory or the induction failure of long-term potentiation in the dorsal CA1 in adult LPS mice. An increase of mIPSCs amplitude was further detected in adult LPS mice indicative of postsynaptic potentiation of GABAergic transmission. Additionally, neonatal LPS resulted in the increased expression and function of K⁺-Cl^--cotransporter 2 (KCC2) and the decreased expression of transforming growth factor-beta 1 (TGF-β1) in the dorsal CA1 during adulthood. The local TGF-β1 overexpression improved KCC2 expression and function, synaptic plasticity and memory of adult LPS mice. Adult LPS mice show hypermethylation of TGFb1 promoter and negatively correlate with reduced TGF-β1 transcripts. 5-Aza-deoxycytidine restored the changes in TGFb1 promoter methylation and TGF-β1 expression. Altogether, the results suggest that hypermethylation-induced reduction of TGF-β1 leads to enhanced GABAergic synaptic inhibition through increased KCC2 expression, which is a underlying mechanism of neonatal inflammation-induced hippocampus-dependent memory impairment in adult mice.

Role of gut-brain axis in neurodevelopmental impairment of necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a common gastrointestinal disease of preterm infants with high morbidity and mortality. In survivors of NEC, one of the leading causes of long-term morbidity is the development of severe neurocognitive injury. The exact pathogenesis of neurodevelopmental delay in NEC remains unknown, but microbiota is considered to have dramatic effects on the development and function of the host brain via the gut-brain axis. In this review, we discuss the characteristics of microbiota of NEC, the impaired neurological outcomes, and the role of the complex interplay between the intestinal microbiota and brain to influence neurodevelopment in NEC. The increasing knowledge of microbial-host interactions has the potential to generate novel therapies for manipulating brain development in the future.

Sex Differences in Neurodevelopmental Disorders: A Key Role for the Immune System

Sex differences are prominent defining features of neurodevelopmental disorders. Understanding the sex biases in these disorders can shed light on mechanisms leading to relative risk and resilience for the disorders, as well as more broadly advance our understanding of how sex differences may relate to brain development. The prevalence of neurodevelopmental disorders is increasing, and the two most common neurodevelopmental disorders, Autism Spectrum Disorder (ASD) and Attention-Deficit/Hyperactivity Disorder (ADHD) exhibit male-biases in prevalence rates and sex differences in symptomology. While the causes of neurodevelopmental disorders and their sex differences remain to be fully understood, increasing evidence suggests that the immune system plays a critical role in shaping development. In this chapter we discuss sex differences in prevalence and symptomology of ASD and ADHD, review sexual differentiation and immune regulation of neurodevelopment, and discuss findings from human and rodent studies of immune dysregulation and perinatal immune perturbation as they relate to potential mechanisms underlying neurodevelopmental disorders. This chapter will give an overview of how understanding sex differences in neuroimmune function in the context of neurodevelopmental disorders could lend insight into their etiologies and better treatment strategies.

Linking the gut microbiome to microglial activation in opioid use disorder

Substance use disorder (SUD) is a physical and psychological disorder globally prevalent today that has resulted in over 107,000 drug overdose deaths in 2021 in the United States alone. This manuscript reviews the potential relationship between opioid use disorder (OUD), a prevalent subset of SUD, and the microglia, the resident macrophages of the central nervous system (CNS), as they have been found to become significantly more activated during opioid exposure. The inflammatory response mediated by the microglia could contribute to the pathophysiology of SUDs, in particular OUD. Further understanding of the microglia and how they respond to not only signals in the CNS but also signals from other areas of the body, such as the gut microbiome, could explain how the microglia are involved in drug use. Several studies have shown extensive communication between the gut microbiome and the microglia, which may be an important factor in the initiation and development of OUD. Particularly, strategies seeking to manipulate and restore the gut microbiome have been shown to reduce microglial activation and attenuate inflammation. In this review, we discuss the evidence for a link between the microglia and OUD and how the gut microbiome might influence microglial activation to drive the disorder and its associated behaviors. Understanding this connection between microglia and the gut microbiome in the context of drug use may present additional therapeutic targets to treat the different stages of drug use.

Isoflurane stress induces region-specific glucocorticoid levels in neonatal mouse brain

The profound programming effects of early life stress (ELS) on brain and behavior are thought to be primarily mediated by adrenal glucocorticoids (GCs). However, in mice, stressors are often administered between postnatal days 2 and 12 (PND2-12), during the stress hyporesponsive period (SHRP), when adrenal GC production is greatly reduced at baseline and in response to stressors. During the SHRP, specific brain regions produce GCs at baseline, but it is unknown if brain GC production increases in response to stressors. We treated mice at PND1 (pre-SHRP), PND5 (SHRP), PND9 (SHRP), and PND13 (post-SHRP) with an acute stressor (isoflurane anesthesia), vehicle control (oxygen), or neither (baseline). We measured a panel of progesterone and six GCs in the blood, hippocampus, cerebral cortex, and hypothalamus via liquid chromatography tandem mass spectrometry. At PND1, baseline corticosterone levels were high and did not increase in response to stress. At PND5, baseline corticosterone levels were very low, increases in brain corticosterone levels were greater than the increase in blood corticosterone levels, and stress had region-specific effects. At PND9, baseline corticosterone levels were low and increased similarly and moderately in response to stress. At PND13, blood corticosterone levels were higher than those at PND9, and corticosterone levels were higher in blood than in brain regions. These data illustrate the rapid and profound changes in stress physiology during neonatal development and suggest that neurosteroid production is a possible mechanism by which ELS has enduring effects on brain and behavior.

Neuroprotective Role of Lactoferrin during Early Brain Development and Injury through Lifespan

Early adverse fetal environments can significantly disturb central nervous system (CNS) development and subsequently alter brain maturation. Nutritional status is a major variable to be considered during development and increasing evidence links neonate and preterm infant impaired brain growth with neurological and psychiatric diseases in adulthood. Breastfeeding is one of the main components required for healthy newborn development due to the many "constitutive" elements breastmilk contains. Maternal intake of specific nutrients during lactation may alter milk composition, thus affecting newborn nutrition and, potentially, brain development. Lactoferrin (Lf) is a major protein present in colostrum and the main protein in human milk, which plays an important role in the benefits of breastfeeding during postnatal development. It has been demonstrated that Lf has antimicrobial, as well as anti-inflammatory properties, and is potentially able to reduce the incidence of sepsis and necrotizing enterocolitis (NEC), which are particularly frequent in premature births. The anti-inflammatory effects of Lf can reduce birth-related pathologies by decreasing the release of pro-inflammatory factors and inhibiting premature cervix maturation (also related to commensal microbiome abnormalities) that could contribute to disrupting brain development. Pre-clinical evidence shows that Lf protects the developing brain from neuronal injury, enhances brain connectivity and neurotrophin production, and decreases inflammation in models of perinatal inflammatory challenge, intrauterine growth restriction (IUGR) and neonatal hypoxia-ischemia (HI). In this context, Lf can provide nutritional support for brain development and cognition and prevent the origin of neuropsychiatric diseases later in life. In this narrative review, we consider the role of certain nutrients during neurodevelopment linking to the latest research on lactoferrin with respect to neonatology. We also discuss new evidence indicating that early neuroprotective pathways modulated by Lf could prevent neurodegeneration through anti-inflammatory and immunomodulatory processes.

Glucocorticoid Production in Lymphoid Organs: Acute Effects of Lipopolysaccharide in Neonatal and Adult Mice

Glucocorticoids (GCs) are critical modulators of the immune system. The hypothalamic-pituitary-adrenal (HPA) axis regulates circulating GC levels and is stimulated by endotoxins. Lymphoid organs also produce GCs; however, it is not known how lymphoid GC levels are regulated in response to endotoxins. We assessed whether an acute challenge of lipopolysaccharide (LPS) increases lymphoid levels of progesterone and GCs, and expression of steroidogenic enzymes and key HPA axis components (eg, corticotropin-releasing hormone [CRH], adrenocorticotropic hormone [ACTH]). We administered LPS (50 µg/kg intraperitoneally) or vehicle control to male and female C57BL/6J neonatal (postnatal day [PND] 5) and adult (PND90) mice and collected blood, bone marrow, thymus, and spleen 4 hours later. We measured progesterone, 11-deoxycorticosterone, corticosterone, and 11-dehydrocorticosterone via liquid chromatography-tandem mass spectrometry. We measured gene expression of key steroidogenic enzymes (Cyp11b1, Hsd11b1, and Hsd11b2) and HPA axis components (Crh, Crhr1, Pomc, and Mc2r) via quantitative polymerase chain reaction. At PND5, LPS induced greater increases in steroid levels in lymphoid organs than in blood. In contrast, at PND90, LPS induced greater increases in steroid levels in blood than in lymphoid organs. Steroidogenic enzyme transcripts were present in all lymphoid organs, and LPS altered steroidogenic enzyme expression predominantly in the spleen. Lastly, we detected transcripts of key HPA axis components in all lymphoid organs, and there was an effect of LPS in the spleen. Taken together, these data suggest that LPS regulates GC production by lymphoid organs, similar to its effects on the adrenal glands, and the effects of LPS might be mediated by local expression of CRH and ACTH.

Establishment of tissue-resident immune populations in the fetus

The immune system establishes during the prenatal period from distinct waves of stem and progenitor cells and continuously adapts to the needs and challenges of early postnatal and adult life. Fetal immune development not only lays the foundation for postnatal immunity but establishes functional populations of tissue-resident immune cells that are instrumental for fetal immune responses amidst organ growth and maturation. This review aims to discuss current knowledge about the development and function of tissue-resident immune populations during fetal life, focusing on the brain, lung, and gastrointestinal tract as sites with distinct developmental trajectories. While recent progress using system-level approaches has shed light on the fetal immune landscape, further work is required to describe precise roles of prenatal immune populations and their migration and adaptation to respective organ environments. Defining points of prenatal susceptibility to environmental challenges will support the search for potential therapeutic targets to positively impact postnatal health.

Early Life Painful Procedures: Long-Term Consequences and Implications for Farm Animal Welfare

Farm animals routinely undergo painful husbandry procedures early in life, including disbudding and castration in calves and goat kids, tail docking and castration in piglets and lambs, and beak trimming in chicks. In rodents, inflammatory events soon after birth, when physiological systems are developing and sensitive to perturbation, can profoundly alter phenotypic outcomes later in life. This review summarizes the current state of research on long-term phenotypic consequences of neonatal painful procedures in rodents and farm animals, and discusses the implications for farm animal welfare. Rodents exposed to early life inflammation show a hypo-/hyper-responsive profile to pain-, fear-, and anxiety-inducing stimuli, manifesting as an initial attenuation in responses that transitions into hyperresponsivity with increasing age or cumulative stress. Neonatal inflammation also predisposes rodents to cognitive, social, and reproductive deficits, and there is some evidence that adverse effects may be passed to offspring. The outcomes of neonatal inflammation are modulated by injury etiology, age at the time of injury and time of testing, sex, pain management, and rearing environment. Equivalent research examining long-term phenotypic consequences of early life painful procedures in farm animals is greatly lacking, despite obvious implications for welfare and performance. Improved understanding of how these procedures shape phenotypes will inform efforts to mitigate negative outcomes through reduction, replacement, and refinement of current practices.

Glucocorticoid production in the thymus and brain: Immunosteroids and neurosteroids

Glucocorticoids (GCs) regulate a myriad of physiological systems, such as the immune and nervous systems. Systemic GC levels in blood are often measured as an indicator of local GC levels in target organs. However, several extra-adrenal organs can produce and metabolize GCs locally. More sensitive and specific methods for GC analysis (i.e., mass spectrometry) allow measurement of local GC levels in small tissue samples with low GC concentrations. Consequently, is it now apparent that systemic GC levels often do not reflect local GC levels. Here, we review the use of systemic GC measurements in clinical and research settings, discuss instances where systemic GC levels do not reflect local GC levels, and present evidence that local GC levels provide useful insights, with a focus on local GC production in the thymus (immunosteroids) and brain (neurosteroids). Lastly, we suggest key areas for further research, such as the roles of immunosteroids and neurosteroids in neonatal programming and the potential clinical relevance of local GC modulators.

Transduction of inflammation from peripheral immune cells to the hippocampus induces neuronal hyperexcitability mediated by Caspase-1 activation

BACKGROUND

Recent studies report infiltration of peripheral blood mononuclear cells (PBMCs) into the central nervous system (CNS) in epileptic disorders, suggestive of a potential contribution of PBMC extravasation to the generation of seizures. Nevertheless, the underlying mechanisms involved in PBMC infiltrates promoting neuronal predisposition to ictogenesis remain unclear. Therefore, we developed an in vitro model mimicking infiltration of activated PBMCs into the brain in order to investigate potential transduction of inflammatory signals from PBMCs to the CNS.

METHODS

To establish our model, we first extracted PBMCs from rat spleen, then, immunologically primed PBMCs with lipopolysaccharide (LPS), followed by further activation with nigericin. Thereafter, we co-cultured these activated PBMCs with organotypic cortico-hippocampal brain slice cultures (OCHSCs) derived from the same rat, and compared PBMC-OCHSC co-cultures to OCHSCs exposed to PBMCs in the culture media. We further targeted a potential molecular pathway underlying transduction of peripheral inflammation to OCHSCs by incubating OCHSCs with the Caspase-1 inhibitor VX-765 prior to co-culturing PBMCs with OCHSCs. After 24 h, we analyzed inflammation markers in the cortex and the hippocampus using semiquantitative immunofluorescence. In addition, we analyzed neuronal activity by whole-cell patch-clamp recordings in cortical layer II/III and hippocampal CA1 pyramidal neurons.

RESULTS

In the cortex, co-culturing immunoreactive PBMCs treated with LPS + nigericin on top of OCHSCs upregulated inflammatory markers and enhanced neuronal excitation. In contrast, no excitability changes were detected after adding primed PBMCs (i.e. treated with LPS only), to OCHSCs. Strikingly, in the hippocampus, both immunoreactive and primed PBMCs elicited similar pro-inflammatory and pro-excitatory effects. However, when immunoreactive and primed PBMCs were cultured in the media separately from OCHSCs, only immunoreactive PBMCs gave rise to neuroinflammation and hyperexcitability in the hippocampus, whereas primed PBMCs failed to produce any significant changes. Finally, VX-765 application to OCHSCs, co-cultured with either immunoreactive or primed PBMCs, prevented neuroinflammation and hippocampal hyperexcitability in OCHSCs.

CONCLUSIONS

Our study shows a higher susceptibility of the hippocampus to peripheral inflammation as compared to the cortex, mediated via Caspase-1-dependent signaling pathways. Thus, our findings suggest that Caspase-1 inhibition may potentially provide therapeutic benefits during hippocampal neuroinflammation and hyperexcitability secondary to peripheral innate immunity.

Maternal immune activation primes deficiencies in adult hippocampal neurogenesis

Neurogenesis, the process in which new neurons are generated, occurs throughout life in the mammalian hippocampus. Decreased adult hippocampal neurogenesis (AHN) is a common feature across psychiatric disorders, including schizophrenia, depression- and anxiety-related behaviours, and is highly regulated by environmental influences. Epidemiological studies have consistently implicated maternal immune activation (MIA) during neurodevelopment as a risk factor for psychiatric disorders in adulthood. The extent to which the reduction of hippocampal neurogenesis in adulthood may be driven by early life exposures, such as MIA, is however unclear. We therefore reviewed the literature for evidence of the involvement of MIA in disrupting AHN. Consistent with our hypothesis, data from both in vivo murine and in vitro human models of AHN provide evidence for key roles of specific cytokines induced by MIA in the foetal brain in disrupting hippocampal neural progenitor cell proliferation and differentiation early in development. The precise molecular mechanisms however remain unclear. Nonetheless, these data suggest a potential latent vulnerability mechanism, whereby MIA primes dysfunction in the unique hippocampal pool of neural stem/progenitor cells. This renders offspring potentially more susceptible to additional environmental exposures later in life, such as chronic stress, resulting in the unmasking of psychopathology. We highlight the need for studies to test this hypothesis using validated animal models of MIA, but also to test the relevance of such data for human pathology at a molecular basis through the use of patient-derived induced pluripotent stem cells (hiPSC) differentiated into hippocampal progenitor cells.

Local injury and systemic infection in infants alter later nociception and pain affect during early life and adulthood

Newborns in intensive care are regularly exposed to minor painful procedures at developmental time points when noxious stimulation would be normally absent. Pain from these interventions is inconsistently treated and often exists concurrently with systemic infection, a common comorbidity of prematurity. Our understanding of the independent and combined effects of early painful experiences and infection on pain response is incomplete. The main goals of this research therefore were to understand how pain and infection experienced early in life influence future nociceptive and affective responses to painful stimuli. Rat pups were infected with E-coli on postnatal day 2 (PN2) and had left hind paw injury with carrageenan on PN3. Standard thermal tests for acute pain, formalin tests for inflammatory pain, and conditioned place aversion testing were performed at different ages to assess the nociceptive and affective components of the pain response. Early E-coli infection and early inflammatory injury with carrageenan both independently increased pain scores following hind paw reinjury with formalin on PN8, with effects persisting into adulthood in the carrageenan exposed group. When experienced concurrently, early E-coli infection and carrageenan exposure also increased conditioned aversion to pain in adults. Effect of sex was significant only in formalin testing, with males showing higher pain scores in infancy and females showing higher pain scores as adults. These findings demonstrate that infection experienced early in life can alter both the nociceptive and affective components of the pain response and that there is a cumulative effect of local and systemic pro-inflammatory processes on the aversive component of pain.

The emerging tale of microglia in psychiatric disorders

As the professional phagocytes of the brain, microglia orchestrate the immunological response and play an increasingly important role in maintaining homeostatic brain functions. Microglia are activated by pathological events or slight alterations in brain homeostasis. This activation is dependent on the context and type of stressor or pathology. Through secretion of cytokines, chemokines and growth factors, microglia can strongly influence the response to a stressor and can, therefore, determine the pathological outcome. Psychopathologies have repeatedly been associated with long-lasting priming and sensitization of cerebral microglia. This review focuses on the diversity of microglial phenotype and function in health and psychiatric disease. We first discuss the diverse homeostatic functions performed by microglia and then elaborate on context-specific spatial and temporal microglial heterogeneity. Subsequently, we summarize microglia involvement in psychopathologies, namely major depressive disorder, schizophrenia and bipolar disorder, with a particular focus on post-mortem studies. Finally, we postulate microglia as a promising novel therapeutic target in psychiatry through antidepressant and antipsychotic treatment.

Traumatic Injury to the Developing Brain: Emerging Relationship to Early Life Stress

Despite the high incidence of brain injuries in children, we have yet to fully understand the unique vulnerability of a young brain to an injury and key determinants of long-term recovery. Here we consider how early life stress may influence recovery after an early age brain injury. Studies of early life stress alone reveal persistent structural and functional impairments at adulthood. We consider the interacting pathologies imposed by early life stress and subsequent brain injuries during early brain development as well as at adulthood. This review outlines how early life stress primes the immune cells of the brain and periphery to elicit a heightened response to injury. While the focus of this review is on early age traumatic brain injuries, there is also a consideration of preclinical models of neonatal hypoxia and stroke, as each further speaks to the vulnerability of the brain and reinforces those characteristics that are common across each of these injuries. Lastly, we identify a common mechanistic trend; namely, early life stress worsens outcomes independent of its temporal proximity to a brain injury.

The effects of early-life immune activation on microglia-mediated neuronal remodeling and the associated ontogeny of hippocampal-dependent learning in juvenile rats

Many neurodevelopmental disorders and associated learning deficits have been linked to early-life immune activation or ongoing immune dysregulation (Laskaris et al., 2016; O'Connor et al., 2014; Frick et al., 2013). Neuroscientists have begun to understand how the maturation of neural circuits allows for the emergence of cognitive and learning behaviors; yet we know very little about how these developing neural circuits are perturbed by certain events, including risk-factors such as early-life immune activation and immune dysregulation. To answer these questions, we examined the impact of early-life immune activation on the emergence of hippocampal-dependent learning in juvenile male and female rats using a well-characterized hippocampal-dependent learning task and we investigated the corresponding, dynamic multicellular interactions in the hippocampus that may contribute to these learning deficits. We found that even low levels of immune activation can result in hippocampal-depedent learning deficits days later, but only when this activation occurs during a sensitive period of development. The initial immune response and associated cytokine production in the hippocampus resolved within 24 h, several days prior to the observed learning deficit, but notably the initial immune response was followed by altered microglial-neuronal communication and synapse remodeling that changed the structure of hippocampal neurons during this period of juvenile brain development. We conclude that immune activation or dysregulation during a sensitive period of hippocampal development can precipitate the emergence of learning deficits via a multi-cellular process that may be initiated by, but not the direct result of the initial cytokine response. SIGNIFICANCE STATEMENT: Many neurodevelopmental disorders have been linked to early-life immune activation or immune dysregulation; however, very little is known about how dynamic changes in neuroimmune cells mediate the transition from normal brain function to the early stages of cognitive disorders, or how changes in immune signaling are subsequently integrated into developing neuronal networks. The current experiments examined the consequences of immune activation on the cellular and molecular changes that accompany the emergence of learning deficits during a sensitive period of hippocampal development. These findings have the potential to significantly advance our understanding of how early-life immune activation or dysregulation can result in the emergence of cognitive and learning deficits that are the largest source of years lived with disability in humans.

What animal models can tell us about long-term cognitive dysfunction following sepsis: A systematic review

Survivors of sepsis often develop long-term cognitive impairments. This review aimed at exploring the results of the behavioral tools and tests which have been used to evaluate cognitive dysfunction in different animal models of sepsis. Two independent investigators searched for sepsis- and cognition-related keywords. 6323 publications were found, of which 355 were selected based on their title, and 226 of these were chosen based on manuscript review. LPS was used to induce sepsis in 171 studies, while CLP was used in 55 studies. Inhibitory avoidance was the most widely used method for assessing aversive memory, followed by fear conditioning and continuous multi-trial inhibitory avoidance. With regard to non-aversive memory, most studies used the water maze, open-field, object recognition, Y-maze, plus maze, and radial maze tests. Both CLP and LPS models of sepsis were effective in inducing short- and long-term behavioral impairment. Our findings help elucidate the mechanisms involved in the pathophysiology of sepsis-induced cognitive changes, as well as the available methods and tests used to study this in animal models.

Trained Immunity: Reprogramming Innate Immunity in Health and Disease

Traditionally, the innate and adaptive immune systems are differentiated by their specificity and memory capacity. In recent years, however, this paradigm has shifted: Cells of the innate immune system appear to be able to gain memory characteristics after transient stimulation, resulting in an enhanced response upon secondary challenge. This phenomenon has been called trained immunity. Trained immunity is characterized by nonspecific increased responsiveness, mediated via extensive metabolic and epigenetic reprogramming. Trained immunity explains the heterologous effects of vaccines, which result in increased protection against secondary infections. However, in chronic inflammatory conditions, trained immunity can induce maladaptive effects and contribute to hyperinflammation and progression of cardiovascular disease, autoinflammatory syndromes, and neuroinflammation. In this review we summarize the current state of the field of trained immunity, its mechanisms, and its roles in both health and disease.

Increased Excitatory Synaptic Transmission Associated with Adult Seizure Vulnerability Induced by Early-Life Inflammation in Mice

Early-life inflammatory stress increases seizure susceptibility later in life. However, possible sex- and age-specific differences and the associated mechanisms are largely unknown. C57BL/6 mice were bred in house, and female and male pups were injected with lipopolysaccharide (LPS; 100 μg/kg, i.p.) or vehicle control (saline solution) at postnatal day 14 (P14). Seizure threshold was assessed in response to pentylenetetrazol (1% solution, i.v.) in adolescence (∼P40) and adulthood (∼P60). We found that adult, but not adolescent, mice treated with LPS displayed ∼34% lower seizure threshold compared with controls. Females and males showed similar increased seizure susceptibility, suggesting that altered brain excitability was age dependent, but not sex dependent. Whole-cell recordings revealed no differences in excitatory synaptic activity onto CA1 pyramidal neurons from control or neonatally inflamed adolescent mice of either sex. However, adult mice of both sexes previously exposed to LPS displayed spontaneous EPSC frequency approximately twice that of controls, but amplitude was unchanged. Although these changes were not associated with alterations in dendritic spines or in the NMDA/AMPA receptor ratio, they were linked to an increased glutamate release probability from Schaffer collateral, but not temporoammonic pathway. This glutamate increase was associated with reduced activity of presynaptic GABA_B receptors and was independent of the endocannabinoid-mediated suppression of excitation. Our new findings demonstrate that early-life inflammation leads to long-term increased hippocampal excitability in adult female and male mice associated with changes in glutamatergic synaptic transmission. These alterations may contribute to enhanced vulnerability of the brain to subsequent pathologic challenges such as epileptic seizures.SIGNIFICANCE STATEMENT Adult physiology has been shown to be affected by early-life inflammation. Our data reveal that early-life inflammation increases excitatory synaptic transmission onto hippocampal CA1 pyramidal neurons in an age-dependent manner through disrupted presynaptic GABA_B receptor activity on Schaffer collaterals. This hyperexcitability was seen only in adult, and not in adolescent, animals of either sex. The data suggest a maturation process, independent of sex, in the priming action of early-life inflammation and highlight the importance of studying mature brains to reveal cellular changes associated with early-life interventions.

Fetal inflammation induces acute immune tolerance in the neonatal rat hippocampus

BACKGROUND

Infants born preterm due to chorioamnionitis are frequently affected by a fetal inflammatory response syndrome (FIRS) and then by subsequent postnatal infections. FIRS and postnatal systemic inflammatory events independently contribute to poor neurocognitive outcomes of preterm infants. Developmental integrity of the hippocampus is crucial for intact neurocognitive outcomes in preterms and hippocampally dependent behaviors are particularly vulnerable to preterm systemic inflammation. How FIRS modulates the hippocampal immune response to acute postnatal inflammatory events is not well understood.

METHODS

Prenatal LPS exposed (FIRS) and control neonatal rats received i.p. LPS or saline at postnatal day (P) 5. On P7, immune response was evaluated in the hippocampus of four treatment groups by measuring gene expression of inflammatory mediators and cytosolic and nuclear NFκB pathway proteins. Microglial activation was determined by CD11b+ and Iba1+ immunohistochemistry (IHC) and inflammatory gene expression of isolated microglia. Astrocyte reactivity was measured using Gfap+ IHC.

RESULTS

Postnatal LPS resulted in a robust hippocampal inflammatory response. In contrast, FIRS induced by prenatal LPS attenuated the response to postnatal LPS exposure, evidenced by decreased gene expression of inflammatory mediators, decreased nuclear NFκB p65 protein, and fewer activated CD11b+ and Iba1+ microglia. Isolated microglia demonstrated inflammatory gene upregulation to postnatal LPS without evidence of immune tolerance by prenatal LPS.

CONCLUSION

Prenatal LPS exposure induced immune tolerance to subsequent postnatal LPS exposure in the hippocampus. Microglia demonstrate a robust inflammatory response to postnatal LPS, but only a partial immune tolerance response.

Steroid profiling of glucocorticoids in microdissected mouse brain across development

Corticosterone is produced by the adrenal glands and also produced locally by other organs, such as the brain. Local levels of corticosterone in specific brain regions during development are not known. Here, we microdissected brain tissue and developed a novel liquid chromatography tandem mass spectrometry method (LC-MS/MS) to measure a panel of seven steroids (including 11-deoxycorticosterone (DOC), corticosterone, and 11-dehydrocorticosterone (DHC) in the blood, hippocampus (HPC), cerebral cortex (CC), and hypothalamus (HYP) of mice at postnatal day (PND) 5, 21, and 90. In a second cohort of mice, we measured the expression of three genes that code for steroidogenic enzymes that regulate corticosterone levels (Cyp11b1, Hsd11b1, and Hsd11b2) in the HPC, CC, and HYP. There were region-specific patterns of steroid levels across development, including higher corticosterone levels in the HPC and HYP than in the blood at PND5. In contrast, corticosterone levels were higher in the blood than in all brain regions at PND21 and PND90. Brain corticosterone levels were not positively correlated with blood corticosterone levels, and correlations across brain regions increased with age. Local corticosterone levels were best predicted by local DOC levels at PND5, but by local DHC levels at PND21 and PND90. Transcripts for the three enzymes were detectable in all samples (with highest expression of Hsd11b1) and showed region-specific changes with age. These data demonstrate that individual brain regions fine-tune local levels of corticosterone during early development and that coupling of glucocorticoid levels across regions increases with age.

Do Adolescent Exposure to Cannabinoids and Early Adverse Experience Interact to Increase the Risk of Psychiatric Disorders: Evidence from Rodent Models

There have been growing concerns about the protracted effects of cannabis use in adolescents on emotion and cognition outcomes, motivated by evidence of growing cannabis use in adolescents, evidence linking cannabis use to various psychiatric disorders, and the increasingly perceived notion that cannabis is harmless. At the same time, studies suggest that cannabinoids may have therapeutic potential against the impacts of stress on the brain and behavior, and that young people sometimes use cannabinoids to alleviate feelings of depression and anxiety (i.e., “self-medication”). Exposure to early adverse life events may predispose individuals to developing psychopathology in adulthood, leading researchers to study the causality between early life factors and cognitive and emotional outcomes in rodent models and to probe the underlying mechanisms. In this review, we aim to better understand the long-term effects of cannabinoids administered in sensitive developmental periods (mainly adolescence) in rodent models of early life stress. We suggest that the effects of cannabinoids on emotional and cognitive function may vary between different sensitive developmental periods. This could potentially affect decisions regarding the use of cannabinoids in clinical settings during the early stages of development and could raise questions regarding educating the public as to potential risks associated with cannabis use.

Vanillic Acid, a Bioactive Phenolic Compound, Counteracts LPS-Induced Neurotoxicity by Regulating c-Jun N-Terminal Kinase in Mouse Brain

The receptor for advanced glycation end products (RAGE), a pattern recognition receptor signaling event, has been associated with several human illnesses, including neurodegenerative diseases, particularly in Alzheimer’s disease (AD). Vanillic acid (V.A), a flavoring agent, is a benzoic acid derivative having a broad range of biological activities, including antioxidant, anti-inflammatory, and neuroprotective effects. However, the underlying molecular mechanisms of V.A in exerting neuroprotection are not well investigated. The present study aims to explore the neuroprotective effects of V.A against lipopolysaccharides (LPS)-induced neuroinflammation, amyloidogenesis, synaptic/memory dysfunction, and neurodegeneration in mice brain. Behavioral tests and biochemical and immunofluorescence assays were applied. Our results indicated increased expression of RAGE and its downstream phospho-c-Jun n-terminal kinase (p-JNK) in the LPS-alone treated group, which was significantly reduced in the V.A + LPS co-treated group. We also found that systemic administration of LPS-injection induced glial cells (microglia and astrocytes) activation and significantly increased expression level of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-KB) and secretion of proinflammatory cytokines including tumor necrosis factor alpha (TNF-α), interleukin-1 β (IL1-β), and cyclooxygenase (COX-2). However, V.A + LPS co-treatment significantly inhibited the LPS-induced activation of glial cells and neuroinflammatory mediators. Moreover, we also noted that V.A treatment significantly attenuated LPS-induced increases in the expression of AD markers, such as β-site amyloid precursor protein (APP)–cleaving enzyme 1 (BACE1) and amyloid-β (Aβ). Furthermore, V.A treatment significantly reversed LPS-induced synaptic loss via enhancing the expression level of pre- and post-synaptic markers (PSD-95 and SYP), and improved memory performance in LPS-alone treated group. Taken together; we suggest that neuroprotective effects of V.A against LPS-induced neurotoxicity might be via inhibition of LPS/RAGE mediated JNK signaling pathway; and encourage future studies that V.A would be a potential neuroprotective and neurotherapeutic candidate in various neurological disorders.

Minocycline differentially modulates human spatial memory systems

Microglia play a critical role in many processes fundamental to learning and memory in health and are implicated in Alzheimer's pathogenesis. Minocycline, a centrally-penetrant tetracycline antibiotic, inhibits microglial activation and enhances long-term potentiation, synaptic plasticity, neurogenesis and hippocampal-dependent spatial memory in rodents, leading to clinical trials in human neurodegenerative diseases. However, the effects of minocycline on human memory have not previously been investigated. Utilising a double-blind, randomised crossover study design, we recruited 20 healthy male participants (mean 24.6 ± 5.0 years) who were each tested in two experimental sessions: once after 3 days of Minocycline 150 mg (twice daily), and once 3 days of placebo (identical administration). During each session, all completed an fMRI task designed to tap boundary- and landmark-based navigation (thought to rely on hippocampal and striatal learning mechanisms respectively). Given the rodent literature, we hypothesised that minocycline would selectively modulate hippocampal learning. In line with this, minocycline biased use of boundary- compared to landmark-based information (t980 = 3.140, p = 0.002). However, though this marginally improved performance for boundary-based objects (t980 = 1.972, p = 0.049), it was outweighed by impaired landmark-based navigation (t980 = 6.374, p < 0.001) resulting in an overall performance decrease (t980 = 3.295, p = 0.001). Furthermore, against expectations, minocycline significantly reduced activity during memory encoding in the right caudate (t977 = 2.992, p = 0.003) and five other cortical regions, with no significant effect in the hippocampus. In summary, minocycline impaired human spatial memory performance, likely through disruption of striatal processing resulting in greater biasing towards reliance on boundary-based navigation.

The role of microglia in the second and third postnatal weeks of life in rat hippocampal development and memory

Microglia are resident immune cells of the central nervous system (CNS). In adulthood they are involved in surveillance and responses to pathogens and injury and prenatally they play a role in brain development. However, the role of microglia during the early postnatal period and how they impact development long-term remains poorly understood. Here, to investigate the specific role of microglia in postnatal development, we used a Cx3cr1-Dtr transgenic Wistar rat model to acutely ablate microglia from either postnatal day (P) 7 or 14. We specifically assessed how transient microglial ablation affected astrocytes and neurons acutely, during the juvenile period, and in adulthood. Hippocampal microglial numbers remained low at P21 in the P7-ablated animals and complexity remained reduced after P14-ablation. This protracted effect on these key immune cells led to a small but significant increase in CA1 mature neuron numbers and a significant increase in astrocyte density in the subgranular dentate gyrus in adults that had their microglia ablated at P14. However, these histological differences were small, and spatial and recognition memory in novel objection and place recognition tests were not affected. Overall, our data reveal for the first time that the transient depletion of microglia during the neonatal period impacts briefly on the brain but that the long-lasting effects are minimal. Neonatal microglia may be dispensable in the establishment of hippocampal brain function. These data also imply that novel therapeutic anti-inflammatories that cross the blood-brain barrier to inhibit microglia are unlikely to have long-term negative consequences if administered in the neonatal period.

Estradiol Increases Microglial Response to Lipopolysaccharide in the Ventromedial Hypothalamus during the Peripubertal Sensitive Period in Female Mice

Sensitive periods are times of development during which the effects of experience are unusually strong and long lasting. The peripubertal period has emerged as one such sensitive period, and a single administration of lipopolysaccharide (LPS) during this time reduces hormone-induced sexual behavior in adult female mice. During periods of high synaptic turnover, maturation, and elimination, as occurs during this sensitive period, microglia are particularly active. Estradiol also regulates microglial numbers, morphology, and activation. In addition, a good deal of evidence suggests that estradiol may confer this vulnerability to the effects of a stressor during the peripubertal period. Therefore, we investigated the effects of estradiol on microglial morphology, cytokine levels, and the sickness response to LPS. Estradiol levels were manipulated by implanting an estradiol-filled SILASTIC capsule (or oil-filled control) in ovariectomized mice or by administering the aromatase inhibitor, formestane (or oil control), to ovary-intact mice. We found that (1) estradiol elevates basal microglial Iba1 immunoreactivity in the ventromedial nucleus of the hypothalamus (VMH), (2) LPS induces higher levels of proinflammatory cytokines in the presence of estradiol, and (3) LPS causes hypothermia in the presence of estradiol. Taken together, these data suggest that estradiol enhances the effect of LPS during the pubertal sensitive period.

Perinatal Opioid Exposure Primes the Peripheral Immune System Toward Hyperreactivity

The increased incidence of opioid use during pregnancy warrants investigation to reveal the impact of opioid exposure on the developing fetus. Exposure during critical periods of development could have enduring consequences for affected individuals. Particularly, evidence is mounting that developmental injury can result in immune priming, whereby subsequent immune activation elicits an exaggerated immune response. This maladaptive hypersensitivity to immune challenge perpetuates dysregulated inflammatory signaling and poor health outcomes. Utilizing an established preclinical rat model of perinatal methadone exposure, we sought to investigate the consequences of developmental opioid exposure on in vitro activation of peripheral blood mononuclear cells (PBMCs). We hypothesize that PBMCs from methadone-exposed rats would exhibit abnormal chemokine and cytokine expression at baseline, with exaggerated chemokine and cytokine production following immune stimulation compared to saline-exposed controls. On postnatal day (P) 7, pup PMBCs were isolated and cultured, pooling three pups per n. Following 3 and 24 h, the supernatant from cultured PMBCs was collected and assessed for inflammatory cytokine and chemokine expression at baseline or lipopolysaccharide (LPS) stimulation using multiplex electrochemiluminescence. Following 3 and 24 h, baseline production of proinflammatory chemokine and cytokine levels were significantly increased in methadone PBMCs (p < 0.0001). Stimulation with LPS for 3 h resulted in increased tumor necrosis factor (TNF-α) and C-X-C motif chemokine ligand 1 (CXCL1) expression by 3.5-fold in PBMCs from methadone-exposed PBMCs compared to PBMCs from saline-exposed controls (p < 0.0001). Peripheral blood mononuclear cell hyperreactivity was still apparent at 24 h of LPS stimulation, evidenced by significantly increased TNF-α, CXCL1, interleukin 6 (IL-6), and IL-10 production by methadone PMBCs compared to saline control PBMCs (p < 0.0001). Together, we provide evidence of increased production of proinflammatory molecules from methadone PBMCs at baseline, in addition to sustained hyperreactivity relative to saline-exposed controls. Exaggerated peripheral immune responses exacerbate inflammatory signaling, with subsequent consequences on many organ systems throughout the body, such as the developing nervous system. Enhanced understanding of these inflammatory mechanisms will allow for appropriate therapeutic development for infants who were exposed to opioids during development. Furthermore, these data highlight the utility of this in vitro PBMC assay technique for future biomarker development to guide specific treatment for patients exposed to opioids during gestation.

Microglial Function in the Effects of Early-Life Stress on Brain and Behavioral Development

The putative effects of early-life stress (ELS) on later behavior and neurobiology have been widely investigated. Recently, microglia have been implicated in mediating some of the effects of ELS on behavior. In this review, findings from preclinical and clinical literature with a specific focus on microglial alterations induced by the exposure to ELS (i.e., exposure to behavioral stressors or environmental agents and infection) are summarized. These studies were utilized to interpret changes in developmental trajectories based on the time at which the stress occurred, as well as the paradigm used. ELS and microglial alterations were found to be associated with a wide array of deficits including cognitive performance, memory, reward processing, and processing of social stimuli. Four general conclusions emerged: (1) ELS interferes with microglial developmental programs, including their proliferation and death and their phagocytic activity; (2) this can affect neuronal and non-neuronal developmental processes, which are dynamic during development and for which microglial activity is instrumental; (3) the effects are extremely dependent on the time point at which the investigation is carried out; and (4) both pre- and postnatal ELS can prime microglial reactivity, indicating a long-lasting alteration, which has been implicated in behavioral abnormalities later in life.

Prenatal opioid exposure: The next neonatal neuroinflammatory disease

The rates of opioid use disorder during pregnancy have more than quadrupled in the last decade, resulting in numerous infants suffering exposure to opioids during the perinatal period, a critical period of central nervous system (CNS) development. Despite increasing use, the characterization and definition of the molecular and cellular mechanisms of the long-term neurodevelopmental impacts of opioid exposure commencing in utero remains incomplete. Thus, in consideration of the looming public health crisis stemming from the multitude of infants with prenatal opioid exposure entering school age, we undertook an investigation of the effects of perinatal methadone exposure in a novel preclinical model. Specifically, we examined the effects of opioids on the developing brain to elucidate mechanisms of putative neural cell injury, to identify diagnostic biomarkers and to guide clinical studies of outcome and follow-up. We hypothesized that methadone would induce a pronounced inflammatory profile in both dams and their pups, and be associated with immune system dysfunction, sustained CNS injury, and altered cognition and executive function into adulthood. This investigation was conducted using a combination of cellular, molecular, biochemical, and clinically translatable biomarker, imaging and cognitive assessment platforms. Data reveal that perinatal methadone exposure increases inflammatory cytokines in the neonatal peripheral circulation, and reprograms and primes the immune system through sustained peripheral immune hyperreactivity. In the brain, perinatal methadone exposure not only increases chemokines and cytokines throughout a crucial developmental period, but also alters microglia morphology consistent with activation, and upregulates TLR4 and MyD88 mRNA. This increase in neuroinflammation coincides with reduced myelin basic protein and altered neurofilament expression, as well as reduced structural coherence and significantly decreased fractional anisotropy on diffusion tensor imaging. In addition to this microstructural brain injury, adult rats exposed to methadone in the perinatal period have significant impairment in associative learning and executive control as assessed using touchscreen technology. Collectively, these data reveal a distinct systemic and neuroinflammatory signature associated with prenatal methadone exposure, suggestive of an altered CNS microenvironment, dysregulated developmental homeostasis, complex concurrent neural injury, and imaging and cognitive findings consistent with clinical literature. Further investigation is required to define appropriate therapies targeted at the neural injury and improve the long-term outcomes for this exceedingly vulnerable patient population.

Impact of inflammation on developing respiratory control networks: rhythm generation, chemoreception and plasticity

The respiratory control network in the central nervous system undergoes critical developmental events early in life to ensure adequate breathing at birth. There are at least three "critical windows" in development of respiratory control networks: 1) in utero, 2) newborn (postnatal day 0-4 in rodents), and 3) neonatal (P10-13 in rodents, 2-4 months in humans). During these critical windows, developmental processes required for normal maturation of the respiratory control network occur, thereby increasing vulnerability of the network to insults, such as inflammation. Early life inflammation (induced by LPS, chronic intermittent hypoxia, sustained hypoxia, or neonatal maternal separation) acutely impairs respiratory rhythm generation, chemoreception and increases neonatal risk of mortality. These early life impairments are also greater in young males, suggesting sex-specific impairments in respiratory control. Further, neonatal inflammation has a lasting impact on respiratory control by impairing adult respiratory plasticity. This review focuses on how inflammation alters respiratory rhythm generation, chemoreception and plasticity during each of the three critical windows. We also highlight the need for additional mechanistic studies and increased investigation into how glia (such as microglia and astrocytes) play a role in impaired respiratory control after inflammation. Understanding how inflammation during critical windows of development disrupt respiratory control networks is essential for developing better treatments for vulnerable neonates and preventing adult ventilatory control disorders.

Microbiota and gut-brain axis dysfunction in autism spectrum disorder: Evidence for functional gastrointestinal disorders

INTRODUCTION

The high frequency of functional gastrointestinal disorders (FGIDs) in autism spectrum disorders (ASD) has drawn attention to the composition of gut microbiota as a possible factor in ASD pathogenesis. However, characterization of a distinctive ASD microbial pattern is still unclear.

OBJECTIVE

To conduct a narrative review on ASD microbial profile and diversity changes relative to NT children and FGID comorbidity and ASD pathogenesis.

METHODOLOGY

First, we searched the PubMed database in peer-reviewed journals for evidence regarding the current epidemiological evidence on FGID comorbidity. For the identification of a microbial profile in ASD children, only original studies examining gut bacterial and fungal abundances and diversity in ASD children and adolescents were included. Lastly, research on the role of microbial dysbiosis as an interface between genetic and environmental risk factors in the pathogenesis of neuropsychiatric disorders, and specifically ASD, was examined.

RESULTS

Prevalence and risk of FGIDs is significantly higher in ASD children and correlates with the severity of ASD. Bacterial and fungal diversity differ between ASD and NT children, indicating a difference in taxonomic abundance profiles, which have been reported at all bacterial phylogenetic levels. However, studies analyzing gut microbiota have a heterogeneous methodology and several limitations that could account for the variety of findings for each taxon. Also, covariate analysis reveals influence of demographics, diet, disease severity, GI comorbidity and allergies. Integration of these findings with changes in metabolome and genetic risk factors allowed for a better understanding of microbiota involvement in ASD pathogenesis for future research.

Alteration of the brain methylation landscape following postnatal inflammatory injury in rat pups

Preterm infants are vulnerable to inflammation-induced white matter injury (WMI), which is associated with neurocognitive impairment and increased risk of neuropsychiatric diseases in adulthood. Epigenetic mechanisms, particularly DNA methylation, play a role in normal development and modulate the response to pathological challenges. Our aims were to determine how WMI triggered DNA methylation alterations in brains of neonatal rats and if such changes persisted over time. We used a robust model of WMI by injecting lipopolysaccharide (LPS) or sterile saline in the corpus callosum of 3-day-old (P3) rat pups. Brains were collected 24 hours (P4) and 21 days post-injection (P24). We extracted genomic DNA from the brain to establish genome-wide quantitative DNA methylation profiles using reduced representation bisulfite sequencing. Neonatal LPS exposure induced a persistent increased methylation of genes related to nervous system development and a reduced methylation of genes associated with inflammatory pathways. These findings suggest that early-life neuroinflammatory exposure impacts the cerebral methylation landscape with determining widespread epigenetic modifications especially in genes related to neurodevelopment.

An IL-6 receptor antagonist attenuates postpartum anhedonia, but has no effect on anhedonia precipitated by subchronic stress in female rats

RATIONALE

Nearly 60-80% of women experience some form of sadness, anxiety, or anhedonia in the weeks following the birth of a child (Patel et al. 23(2):534-42, 2012; Degner 10: 359;j4692, 2017); however, the exact mechanisms that precipitate these changes in mood postpartum are still unknown. It is well-known that the function of the peripheral immune system is significantly altered during pregnancy in order to protect the developing fetus from being rejected by the maternal immune system (Fallon et al. 17(1):7-17, 2002), and we have recently found a dramatic change in the central immune system during and just after pregnancy in female rats (Sherer et al. 66:201-209, 2017). We observed anhedonia in Sprague-Dawley rat dams on the day of birth that is associated with an increase in interleukin (IL)-6 expression in the brain on the day of birth (Posillico and Schwarz 298(Pt B):218-28, 2016).

OBJECTIVES

The goal of the current experiments was to determine whether inhibiting the IL-6 receptor could prevent onset of this postpartum anhedonia, or anhedonia precipitated by subchronic stress in non-pregnant females.

RESULTS

Treatment with an IL-6 receptor antibody attenuated postpartum anhedonia as characterized by a decrease in sucrose preference. In contrast, this antibody had no effect on the decrease in sucrose preference induced following a week of forced swim stress in non-pregnant female rats.

CONCLUSIONS

The results of these studies suggest that the molecular mechanisms that underlie the onset of anhedonia following birth or mild stress in female rats may be distinct.

Exposure to in utero inflammation increases locomotor activity, alters cognitive performance and drives vulnerability to cognitive performance deficits after acute immune activation

Fetal exposure to intrauterine inflammation (IUI) affects brain development. Using intrauterine lipopolysaccharide (LPS) administration to induce a localized, rather than a systemic, inflammation, we have previously shown that IUI increases cytokine expression and microglia number, and reduces white matter in the brains of exposed offspring. Clinical data suggest that IUI may increase the risk for cognitive and neurodevelopmental disorders, however, IUI is often found in the context of preterm birth, making it difficult to disentangle the adverse effects of inflammation from those related to prematurity. Therefore, using a mouse model of IUI that does not involve preterm birth, operant tasks were used to evaluate motivation, attention, impulsivity, and locomotion. IUI-exposed offspring were found to have increased locomotion and increased motivation (females only), and testing in the 5-choice serial reaction time task (5-CSRTT) showed that IUI-exposed offspring performed more trials and could respond accurately at a shorter stimulus length. We have previously shown that IUI animals have a potentiated cytokine response to a "second hit" (acute LPS injection) in adulthood, so animals' performance in the 5CSRTT was evaluated following an acute injection of LPS. As opposed to the improved performance observed under baseline conditions, IUI exposed animals demonstrated a greater decrease in performance after an acute LPS administration. To identify putative molecular mechanisms underlying this potentiated decline in cognitive performance, PFC samples were collected immediately after post-LPS cognitive testing and targeted gene expression analysis was correlated with specific measures of cognitive performance. Three receptors important for neuron-microglia crosstalk were found to correlate with task performance in the males following acute LPS administration. These data demonstrate that early life exposure to localized inflammation of the uterus, in the absence of prematurity, increases locomotor activity and improves some aspects of cognitive performance, but drives a vulnerability for adult cognitive performance deficits in response to acute infection.